Photoelectric sensor having special display features

ABSTRACT

A photoelectric sensor is disclosed that comprises a sensor unit having a casing. The casing includes one surface having a first display and a second display. The first display is structured and arranged to display a threshold value that may be set by an operator of the photoelectric sensor. The second display is structured and arranged to display the actual conditions sensed by said photoelectric sensor. The sensor also includes a selection device for selecting different operational values to display on the second display. The selection device can include a mechanism disposed on the casing for changing the different operational values on the second display. The selection device can also include an adjustment switch disposed on the casing. The adjustment switch allows the operator to adjust the threshold value shown on the first display while the second display shows at least one of the actual conditions sensed by the photoelectric sensor. The photoelectric sensor can be an integrated sensor or can include at least two parts, namely a sensor head and a main body unit. The sensor also can have a plurality of different display setting modes that can be shown on the displays and an operator may set these modes. These different modes include a power setting mode, a hold setting mode and a timer setting mode, each of which can have a plurality of displayable conditions.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a photoelectric sensor having aspecialized display.

[0003] 2. Discussion of the Related Art

[0004] Photoelectric sensors are typically used for detecting objects.They compare a measured quantity, such as reflected light, with athreshold value to determine whether the object is present or not.

[0005] These sensors have a display that can indicate the value of themeasured quantity or simply indicate whether the object is present ornot. Some sensors include a display that can show the value of themeasured quantity and this display can be switched to also show thethreshold value. Before the present invention, it was difficult for theoperator to easily compare a selected measured quantity with thethreshold value since the threshold value was not displayed when theoperator selected the display to show a selected measured quantity.Thus, it was difficult for the operator to easily adjust the thresholdvalue based on the real situation that the photoelectric sensor wasexperiencing. This situation has caused difficulties for the operatorbecause they were required to switch back and forth between displayingthe selected measured value and the threshold value.

SUMMARY OF THE INVENTION

[0006] An object of the invention is to provide a photoelectric sensorthat can simultaneously display multiple parameters related to thesensing conditions.

[0007] A further object of the invention is to provide a photoelectricsensor that allows easy adjustment of a threshold value.

[0008] In one aspect of the invention, there is provided a photoelectricsensor comprising a sensor unit having a casing, the casing includingone surface having a first display and a second display. The firstdisplay is structured and arranged to display a threshold value that maybe set by an operator of the photoelectric sensor. Further, the seconddisplay is structured and arranged to display actual conditions sensedby said photoelectric sensor. The sensor also includes a selectiondevice for selecting different operational values to display on thesecond display. The selection device includes a mechanism disposed onthe casing for changing the different operational values on the seconddisplay.

[0009] In a second aspect of the invention, there is provided aphotoelectric sensor comprising a sensor unit having a casing includingone surface that has a first display and a second display. The firstdisplay is structured and arranged to display a threshold value that maybe set by an operator of the photoelectric sensor and the second displayis structured and arranged to display actual conditions sensed by thephotoelectric sensor. An adjustment switch is also disposed on thecasing. The adjustment switch allows for adjustment of the thresholdvalue shown on the first display while the second display shows at leastone of the actual conditions sensed by the photoelectric sensor.

[0010] In a third aspect of the invention, there is provided aphotoelectric sensor comprising a main body unit and a sensor head unitconnected by at least one cable. At least one of the main body unit andthe sensor head unit includes a casing including one surface that has afirst display and a second display. The first display is structured andarranged to display a property set by an operator of the photoelectricsensor and the second display is structured and arranged to displayactual conditions sensed by said photoelectric sensor. A selectiondevice is also provided for selecting different operational values todisplay on the second display. The selection device can include amechanism like a mode selection switch disposed on the casing forchanging the different operational values shown on the second display.Methods of operating the photoelectric sensor are also disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above objects and features of the present invention will beapparent to those skilled in the art from the following description ofthe preferred embodiments thereof when considered in conjunction withthe appended drawings in which:

[0012]FIG. 1 is a perspective view of a photoelectric sensor comprisinga sensor head unit and an amplifier unit in accordance with a firstembodiment of the present invention.

[0013]FIG. 2 is a block diagram showing the structure of thephotoelectric sensor according to the first embodiment of the e1 presentinvention.

[0014]FIG. 3A is a graph used to explain the process of determining areceived light signal and a threshold value.

[0015]FIG. 3B is an additional graph used to explain the process ofdetermining a received light signal and a threshold value.

[0016]FIG. 4 is a schematic drawing of a circuit of an LED lightingcircuit.

[0017]FIG. 5 is a flowchart showing a process for changing the displaymode of the second display portion according to the first embodiment ofthe present invention.

[0018]FIG. 6 is a flowchart showing a process for changing the displayafter the display mode is selected by the setting switch according tothe first embodiment of the present invention.

[0019]FIG. 7 is a flowchart showing a subroutine procedure thatinterrupts the main routine described in FIG. 6 in accordance with thefirst embodiment of the present invention.

[0020]FIG. 8 is a graph of time versus the quantity of received lightused to explain a principle of the hold mode.

[0021]FIG. 9A is a schematic view of a display side surface of thephotoelectric sensor illustrating one type of display for the first andsecond displays according to the present invention.

[0022]FIG. 9B is a schematic view of a display side surface of thephotoelectric sensor illustrating another type of display for the firstand second displays according to the present invention.

[0023]FIG. 9C is a schematic view of a display side surface of thephotoelectric sensor illustrating yet another type of display for thefirst and second displays according to the present invention.

[0024]FIG. 10 is a schematic representation of how the second displaycan change according to the present invention.

[0025]FIG. 11 is a schematic diagram showing the head unit of thephotoelectric sensor using a triangulation principle as a secondembodiment of the present invention.

[0026]FIGS. 12A and 12B are graphs explaining a determination process byusing the signals N and F outputted from a PSD. FIG. 12A shows when thelevel LV of the positioning signal is equal to or higher than apredetermined threshold value TH. FIG. 12B shows when the level LV ofthe positioning signal is lower than the value TH.

[0027]FIG. 13 is a perspective view of a head unit of a photoelectricsensor of the separate type in accordance with a third embodiment of thepresent invention.

[0028]FIG. 14 is a block diagram showing a structure of the separatetype photoelectric sensor shown in FIG. 13.

[0029]FIG. 15 is a perspective view of a photoelectric sensor comprisingan integrated sensor head unit and amplifier unit in accordance with afurther embodiment of the present invention.

[0030]FIG. 16 is a schematic view of a display side surface of thephotoelectric sensor illustrating additional display types for the firstand second displays according to the present invention.

[0031]FIG. 17 is a schematic view of a display side surface of thephotoelectric sensor illustrating another type of display when switchingthe power mode according to the present invention.

[0032]FIG. 18 is a schematic view of a display side surface of thephotoelectric sensor illustrating yet another type of display whenswitching the detection mode according to the present invention.

[0033]FIG. 19 is a schematic view of a display side surface of thephotoelectric sensor illustrating yet another type of display whenswitching the timer mode according to the present invention.

[0034]FIG. 20 is a schematic view of a display side surface of thephotoelectric sensor illustrating yet another type of display whenswitching the timer setting according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Embodiments of the present invention are described in furtherdetail with reference to the accompanying drawings.

[0036]FIG. 1 is a perspective view of a reflective type photoelectricsensor-comprising a sensor head unit 1 and an amplifier unit 2 inaccordance with a first embodiment of the present invention.

[0037] As shown in FIG. 1, the sensor comprises a sensor head unit 1 anda main body unit 2 including an amplifier. The head unit 1 is connectedto the main body unit 2 by using cables 31 a and 31 b.

[0038] An emitting portion that emits a laser beam to an object to bedetected and a beam receiving portion that receives a reflected beamfrom the detected object are both installed in a casing 11 of the sensorhead unit 1.

[0039] The upper surface of the casing 11 has a detection ratio displayportion 12 comprising a bar type display and a laser emission indicator13. The detection ratio means the ratio of thequantity-of-received-light with respect to a threshold value. In otherwords, the detection ratio indicates a relative quantity (margin) oflight received with respect to the threshold.

[0040] The display portion 12 comprises three LEDs (Laser EmissionDiodes) 12 a, 12 b and 12 c for indicating the detection ratio that willbe described hereinafter.

[0041] The laser emission indicator 13 indicates whether or not thelaser diode of the emitting portion is turned on.

[0042] An upper surface of a casing 21 of the main body unit 2 has afirst display portion 23, a second display portion 22, a bar LED monitor24, a laser emission indicator 25, hold mode indicators 27A and 27B, anadjustment switch 28, a setting switch 29 and a display select or modeswitch 32.

[0043] The hold mode indicator 27A is turned on when one hold mode isset so as to hold a maximum value corresponding to the quantity ofreceived light or corresponding to the detection ratio during apredetermined period by a mode selection operation that will bedescribed later.

[0044] On the other hand, the hold mode indicator 27B is turned on whenanother hold mode is set for holding a minimum value corresponding tothe quantity of received light or corresponding to the detection ratioduring a predetermined period by the mode selection operation.

[0045] The second display portion 22 comprises four digit number displayportions each of which comprises a seven segment LED and displaysnumerals indicating the quantity of received light that is received fromthe laser receiving portion of the head unit 1.

[0046] The display select switch 32 can cyclically change the numeralscorresponding to the quantity of received light displayed on the seconddisplay portion 22 to other numerals. These display options includeindicating a detection ratio of the quantity of received light withrespect to the threshold value and the value corresponding to themaximum value or the minimum value of the quantity of the received lightas well as a relative value corresponding to the maximum value or theminimum value with respect to the threshold value.

[0047] The first display portion 23 also comprises four digit numberdisplay portions each of which comprises a seven segment LED tonumerically display the threshold value.

[0048] The adjustment switch 28 is used to adjust the threshold valuedisplayed on the first display portion 23. The setting switch 29 is usedto set the threshold value.

[0049] The setting switch 29 is initially pushed when the detectedobject is disposed in a predetermined detectable area and the settingswitch 29 is pushed again when the detected object is not disposed inthe predetermined detectable area. The threshold value is then setautomatically to an intermediate value between the value of the quantityof received light with the object in the predetermined detectable areaand the value of the quantity of received light without the object inthe predetermined detectable area.

[0050] Namely, the threshold value becomes one criteria to detect theobject disposed in the predetermined detectable area. The set thresholdvalue can then be displayed on the first display portion 23.

[0051] After the threshold value displayed on the first display portion23 is adjusted by using the adjustment switch 28, the adjusted thresholdvalue is set as a renewed threshold value.

[0052] The second display portion 22 numerically displays the quantityof received light input to the head unit 1. On the other hand, the firstdisplay portion 23 numerically displays a set value like the thresholdvalue that is calculated in the main body unit 2 and is compared withthe quantity of received light.

[0053] The bar LED monitor 24 displays the current value of receivedlight intensity relative to the setting value within a range, typically−15% to +15%.

[0054] The side surface of the casing 21 of the main body unit 2 isconnected to an output cable 30. The output cable 30 outputs a detectionsignal indicating the detected result corresponding to a confirmation ofthe detected object's existence within the detectable area.

[0055]FIG. 2 is a block diagram showing the structure of thephotoelectric sensor according to the first embodiment of the presentinvention. Further, FIG. 3 is a graph explaining the process ofdetermining the existence of the object using the received light signaland the threshold value.

[0056] The head unit 1 has a laser driving circuit 101, a laser diode102, a photo-diode for monitoring 103, a photo-diode 104, a lightreceiving circuit 105, a power supply circuit 106 and a LED lightingcircuit 107. The LED lighting circuit 107 includes the detection ratiodisplay portion 12. The main body unit 2 has a CPU 201, a displayportion 202, an operation portion 203, a variable power source circuit204, a transistor 205, an amplifier 206, an A/D converter 207 and anoutput circuit 208.

[0057] The display portion 202 has the first display portion 23, thesecond display portion 22, the bar LED monitor 24, the laser emissionindicator 25 and the hold mode indicators 27A and 28B. The operationportion 203 has the adjustment switch 28, the setting switch 29 and thedisplay select switch 32.

[0058] The CPU 201 of the main body unit 2 provides a pulse signal PLSto a base terminal of the transistor 205 to control the lighting of thediode 102.

[0059] The transistor 205 is turned on and off corresponding to thepulse signal PLS.

[0060] The collector terminal of the transistor 205 is connected to thelaser driving circuit 101 of the head unit 1 by way of the cable 31 a.

[0061] Thus, the laser driving circuit 101 drives the laser diode 102corresponding to the pulse signal PLS output from the CPU 201. When thelaser diode 102 is turned on, the laser beam is emitted to thepredetermined detectable area. The photo-diode for monitoring 103 isused to monitor the laser beam quantity emitted from the laser diode102.

[0062] When an object 500 to be detected is in the predetermineddetectable area, the photo-diode 104 receives the reflected light fromthe object. The light receiving circuit 105 outputs an analoglight-receiving signal RS corresponding to the quantity of lightreceived by the photo-diode 104.

[0063] The signal RS that is output from the light receiving circuit 105is provided to the main body unit 2 by way of the cable 31 b. Theamplifier 206 of the main body unit 2 amplifies the signal RS outputfrom the light receiving circuit 105 and provides the amplified signalto the A/D converter 207. The A/D converter 207 converts the amplifiedsignal RS from an analog signal to a digital signal and provides thedigital signal LS to the CPU 201. The CPU 201 determines whether theobject 500 is in the predetermined area or not based on a comparison ofthe level of the signal LS provided by the A/D converter 207 with thethreshold value TH. The output circuit 208 then outputs a determinationsignal DT indicating the results of the determination to the outputcable 30.

[0064] The CPU 201 has the threshold value TH set by using theaforementioned method along with the setting switch 29 of the operationportion 203. When it is necessary to adjust the threshold value TH, thisis carried out by operation of the adjustment switch 28.

[0065] When an operator adjusts the threshold value TH, the operator canadjust the threshold value displayed numerically on the first displayportion 23 which is read out from the CPU 201 by using up and downbuttons of the adjustment switch 28 to increment or decrement thedisplayed threshold value TH on the first display portion 23 to adesired value. The operator can also look at the quantity of receivedlight or the detection ratio displayed on the second display portion 22at the same time.

[0066] In other words, since the operator can adjust the threshold valueTH while looking at the current quantity of received light, the operatorcan easily adjust the desirable threshold value.

[0067] Further, the threshold value TH memorized in the CPU 201 is alsochanged prior to changing the displayed numerals of the first displayportion 23. Furthermore, the CPU 201 always manages the adjustmentfunction of the adjustment switch 28.

[0068] Since there is a possibility for the threshold value to bechanged by improper operation of the adjustment switch 28 due to anunintended operator's activity, the photoelectric sensor has a key-lockfunction to lock the adjustment switch 28.

[0069] In detail, pushing the select switch 32 and the adjustment switch28 at the same time for three seconds and more carries out the locksetting of the key-lock function.

[0070] Further, the key-lock function can also be designed to lock otherswitches of the operation portion 203.

[0071] To release the key-lock function, one uses the same operationmentioned above.

[0072]FIGS. 3A and 3B are graphs explaining the process of determiningthe existence of the object using the received light signal and thethreshold value. As shown in FIG. 3A, when the level LV of the receivinglight signal LS is higher than the threshold value TH, it is determinedthat the object 500 is within the detectable area. On the other hand, asshown in FIG. 3B, when the level LV of the receiving light signal LS islower than the threshold value TH, it is determined that the object 500is not within the detectable area.

[0073] When the display select switch 32 of the operation portion 203 ispushed, the CPU 201 calculates the ratio of the level LV correspondingto the quantity of received light with respect to the threshold value THand outputs the result of the calculation to the second display portion22 to display the ratio on the second display portion 22.

[0074] In the case shown in FIG. 3A, the detection ratio is displayed asa number which is larger than “1”. In the other case shown in FIG. 3B,the detection ratio is displayed as a number which is smaller than “1”.Further, the detection ratio can be displayed as a percentage based onthe threshold value being 100%. The CPU 201 provides a control signal DPcorresponding to the calculated detection ratio to the variable powercircuit 204.

[0075] The variable power supply circuit 204 provides a variable voltageVA corresponding to the control signal DP to the head unit 1 through thecable 31 a.

[0076] When the detection ratio is larger, the level of the variablevoltage VA is lower. On the other hand, when the detection ratio islower, the level of the variable voltage VA is higher. Namely, the levelof the variable voltage VA expresses a function of the detection ratio.

[0077] This variable voltage VA is provided to the laser driving circuit101, the fixed power supply circuit 106 and the LED lighting circuit107.

[0078] The fixed power supply circuit 106 receives the variable voltageVA and provides a fixed standard voltage Vref to the laser drivingcircuit 101, the light receiving circuit 105 and the LED lightingcircuit 107.

[0079] Further, the laser driving circuit 101 controls the lightquantity to the laser diode 102 as a fixed quantity based on the currentthrough the photo-diode for monitoring 103 in spite of the level of thevariable voltage VA.

[0080] The LED lighting circuit 107 turns on and off the variousdetection ratio display LEDs 12 a, 12 b and 12 c corresponding to thelevel of the variable voltage VA.

[0081]FIG. 4 is a schematic drawing of the LED lighting circuit 107.

[0082] As shown in FIG. 4, the LED light circuit 107 has resistors R1,R2, R3, R4, R11, R12 and R13, comparators 111, 112 and 113 and detectionratio display LEDs 12 a, 12 b and 12 c.

[0083] The resistors R1, R2, R3 and R4 are disposed in a row between apower supply terminal NV receiving the variable voltage VA and agrounding terminal.

[0084] One input terminal of the comparator 111 is connected to a nodeN1 disposed between the resistors R1 and R2. One input terminal of thecomparator 112 is connected to a node N2 disposed between the resistorsR2 and R3. One input terminal of the comparator 113 is connected to anode N3 disposed between the resistances R3 and R4.

[0085] The other input terminals of the comparators 111, 112 and 113 areconnected to a power supply terminal NR, respectively.

[0086] The output terminal of the comparator 111 is connected to thepower supply terminal NR by way of the detection ratio display LED 12 cand the resistor R11, the output terminal of the comparator 112 isconnected to the power supply terminal NR by way of the detection ratiodisplay LED 12 b and the resistor R12 and the output terminal of thecomparator 113 is connected to the power supply terminal NR by way ofthe detection ratio display LED 12 a and the resistor R13.

[0087] Each of the comparators 111, 112 and 113 compares each electricalpotential at the nodes N1, N2 and N3 with the standard voltage Vref.

[0088] When the variable voltage VA becomes lower than a first levelthis means it is at the lowest level and all the electrical potential ofthe nodes N1, N2 and N3 becomes lower than the standard voltage Vref.Thus the output signals of the comparators 111, 112 and 113 becomelow-level signals.

[0089] As a result, the current through the detection ratio display LEDs12 a, 12 b and 12 c is turned on.

[0090] When the variable voltage VA is positioned between the firstlevel and a second level, where the second level is higher than thefirst level, this means it is at a second lower level and the electricalpotential of the nodes N2 and N3 becomes lower than the standard voltageVref. Thus the output signals of the comparators 112 and 113 becomelow-level signals.

[0091] As a result, the current is through the detection ratio displayLEDs 12 a and 12 b and the detection ratio display LEDs 12 a and 12 bare turned on.

[0092] When the variable voltage VA is positioned between the secondlevel and a third level, which is higher than the first and secondlevels, this means it is at a third lower level and the electricalpotential of the node N3 becomes lower than the standard voltage Vref.Thus the output signal of the comparator 113 becomes a low-level signal.

[0093] As a result, the current is through the detection ratio displayLED 12 a and the detection ratio display LED 12 a is turned on.

[0094] When the variable voltage VA becomes higher than the third lowerlevel this means it is at the highest level and all electrical potentialof the nodes N1, N2 and N3 become higher than the standard voltage Vref.This means that the electrical potential of the node N3 becomes higherthan the standard voltage Vref, and then all of the output signals ofthe comparators 111, 112 and 113 become high-level signals.

[0095] As a result, the detection ratio display LEDs 12 a, 12 b and 12 care not turned on.

[0096] Thus, for example, when the value of the detection ratio is equalto or higher than (110%), all of the three detection ratio display LEDs12 a, 12 b and 12 c are turned on.

[0097] When the value of the detection ratio is equal to or higher than1 (100%), two detection ratio display LEDs 12 a and 12 b are turned on.When the value of the detection ratio is equal to or higher than 0.9(90%) and lower than 1 (100%), the detection ratio display LED 12 a isturned on.

[0098] When the value of the detection ratio is lower than 0.9 (90%),none of the detection ratio display LEDs 12 a, 12 b and 12 c are turnedon.

[0099] Especially, when the detection ratio is higher than 1.1 (110%)and all of the display LEDs 12 a, 12 b and 12 c are turned on, thevariable voltage VA is the lowest. Therefore, when the sensor has astable condition, especially when the set threshold value is at thestable detecting position, the thermal energy made by the head unit 1can be restricted. Thus, this also prevents a decline in performance ofthe laser diode 102 due to heat generated by the head unit 1.

[0100]FIGS. 5, 6 and 7 are flowcharts showing the process of changingthe display of the second display portion 22 of the main body unit 2.

[0101] Using the display select switch 32 and the adjustment switch 28changes can be made to the displayed item of the second display portion22.

[0102] When the CPU 201 receives inputs from the display select switch32 and the adjustment switch 32, the CPU 201 cyclically changes thenumerals displayed on the second display portion 22 from the numeralscorresponding to the input signal LS from the A/D converter 207indicating the quantity of the received light to: the numeralscorresponding to the detection ratio value of the signal LS with respectto the threshold value TH; then to the maximum or minimum value of thequantity of the received light held by the hold mode function; and thento the relative value corresponding to the maximum or minimum value ofthe detection ratio value with respect to the threshold value TH.

[0103]FIG. 5 is a flowchart showing a first mode for changing thedisplay of the second display portion 22 according to the firstembodiment of the present invention. The first mode for changing thedisplay is carried out between displaying the quantity of the receivedlight and the detection ratio. Pushing on the display select switch 32carries out the step of changing the display.

[0104] As shown in FIG. 5, at step S1, when the display select switch 32is pushed, it is determined whether or not the currently displayednumerals correspond to the quantity of received light.

[0105] When it is determined that the currently displayed numeralscorrespond to the quantity of received light at Step S1, the display ischanged to display the numerals corresponding to the current detectionratio at Step S2.

[0106] On the other hand, when it is determined that the currentlydisplayed numerals do not correspond to the quantity of received lightat Step S1, the display is changed to display the numerals correspondingto the quantity of received light at Step S3.

[0107] Namely, the display select switch 32 carries out the change ofthe displayed numerals on the display portion 22 so as to switch betweenthe quantity of received light and the detection ratio.

[0108] The hold mode as a second display change mode will be describedwith respect to FIGS. 6 and 9A-9C. Prior to entering the second displaychange mode, the first display portion 23 displays the threshold valueand the second display portion 22 displays the quantity of the receivedlight or the detection ratio which are selected by the first displaychange mode.

[0109] Then, in this situation, the CPU 201 recognizes the seconddisplay change mode when the display select switch 32 is pushed forthree seconds or more. Thus the CPU 201 changes the displays of thefirst and second display portions 23 and 22 as shown in FIG. 9A.

[0110] In a detail, the display of the first display portion 23 changesfrom the displayed threshold value of the first mode to “std”. Thismeans an initial condition of the second mode or the no-hold modecondition of the hold mode as the second mode. Also the display of thesecond display portion 22 changes from the displayed quantity ofreceived light or the displayed detection ratio at the first mode to“dsp”. This means the current mode is in the second mode.

[0111] Next, when one of the adjustment switches 28 is pushed with theabove-mentioned condition, the displays of the first and second displayportions cyclically change to the display shown in FIG. 9B and FIG. 9C.Further, when one of the switches 28 is pushed again, the displays ofthe first and second display portions change again to the displays shownin FIG. 9A.

[0112] In other words, the display of the first display portion 23cyclically changes between “PH”, “bH” and “std” and the display of thesecond display portion 22 maintains the display “dsp”.

[0113] The “PH” displayed on the first display portion 23 as shown inFIG. 9B means a peak hold value, in other words, it means the maximumvalue. The “bH” shown in FIG. 9C means a bottom hold, in other words, itmeans the minimum value.

[0114] Further, “std” shown in FIG. 9A means a standard or a no-holdmode condition.

[0115] In other words, the displays of the first and second displayportions as shown in FIG. 9A indicate a no-hold mode or an initialcondition. The displays of the first and second display portions asshown in FIG. 9B indicate a maximum value display hold mode. Further,the displays of the first and second display portions as shown in FIG.9C indicate a minimum value display hold mode.

[0116] On the other hand, when the other of the adjustment switches 28is pushed with the above-mentioned condition, the displays of the firstand second display portions change to the displays shown in FIGS. 9C andFIG. 9B, in turn. Further, if the other of the switches 28 is pushedagain, the displays of the first and second display portions changeagain to the displays shown in FIG. 9A.

[0117] In other words, the display of the first display portion 23cyclically changes between “bH”, “PH” and “std” and the display of thesecond display portion 22 maintains the display of “dsp”.

[0118] Then, the operator selects a desired condition from among themaximum and minimum value display hold modes shown in FIGS. 9B and 9C byusing the adjustment switch 28.

[0119] In detail, after the desired condition is selected by one of theswitches 28, the setting switch 29 is pushed to send the modedetermination signal to the CPU 201. When the maximum value display modeis selected, the hold mode indicator 27A is turned on at the same time.

[0120] On the other hand, when the minimum value display mode isselected, the hold mode indicator 27B is turned on at the same timeinstead of the indicator 27A.

[0121]FIG. 6 is a flowchart showing the changes in the display after thedisplay mode is determined by the setting switch 29 as described above.

[0122] The display condition is determined by pushing the setting switch29 and the flow proceeds to Step S4. At this time, the first displayportion 23 displays numerals corresponding to the threshold value THinstead of “PH” or “bH” which is selected and determined by the switches28 and 29. Further, the second display portion 22 displays numeralscorresponding to the selected maximum or minimum value display conditioninstead of “dsp”.

[0123] At Step S4, the set mode is evaluated. In detail, when it isdetermined that the set condition is in the maximum value hold modewhich holds the maximum value of the quantity of the received light anddisplays this value, the flow proceeds to Step S5.

[0124] On the other hand, if it is determined in Step S4 that the setcondition is in the minimum value hold mode which holds the minimumvalue of the quantity of the received light and displays this value, theflow proceeds to Step S13.

[0125] At Step S5, the second display portion 22 continues to displaythe numerals corresponding to the maximum value of the quantity of thereceived light which is renewed at each predetermined term. At the sametime, the first display portion 23 displays the current threshold value.

[0126] When the display select switch 32 is pushed at Step S5, it isdetermined that the display select switch 32 was pushed in Step S6.Then, the flow proceeds to Step S7 where the display of the seconddisplay portion 22 is changed from the maximum value of the quantity ofthe received light to the detection ratio of the current quantity of thereceived light with respect to the threshold value. At this time, thefirst display portion 23 maintains its display of the current thresholdvalue. On the other hand, when it is determined that the display selectswitch 32 was not pushed in Step S6 and the flow returns to Step S5 tokeep the maximum value of the quantity of the received light as thedisplayed numerals on the second display portion 22.

[0127] When the second display portion 22 displays the detection ratioand if it is determined in Step S8 that the display select switch 32 waspushed, the display of the second display portion 22 is changed from thedetection ratio to the maximum value of the detection ratio at eachpredetermined term in Step S9. At this time, the first display portion23 maintains its display of the current threshold value. On the otherhand, when it is determined that the display select switch 32 was notpushed in Step S8, the flow returns to Step S7 to maintain the detectionratio as the display on the second display portion 22.

[0128] When the second display portion 22 displays the maximum value ofthe detection ratio and it is determined that the display select switch32 was pushed in Step S10, the display of the second display portion 22is changed from the maximum value of the detection ratio to the currentquantity of the received light at Step S11. At this time, the firstdisplay portion 23 maintains its display of the current threshold value.On the other hand, when it is determined that the display select switch32 was not pushed in Step S10, the flow returns to Step S9 to maintainthe maximum value of the detection ratio as the display on the seconddisplay portion 22.

[0129] When the second display portion 22 displays the current quantityof the received light and if it is determined that the display selectswitch 32 was pushed in Step S12, the display of the second displayportion 22 is changed from the current quantity of the received light tothe maximum value of the quantity of the received light in Step S5. Atthis time, the first display portion 23 maintains its display of thecurrent threshold value. On the other hand, when it is determined thatthe display select switch 32 was not pushed in Step S12, the flowreturns to Step S11 to keep the current quantity of the received lightas the display on the second display portion 22.

[0130] In other words, the display of the second display portion 22 iscyclically changed from “the maximum value of the quantity of thereceived light” to “the detection ratio” to “the maximum value of thedetection ratio” to “the quantity of the received light” and then backto “the maximum value of the quantity of the received light” in turn bypushing the display select switch 32.

[0131] Further, when the step proceeds to Step S13, the second displayportion 22 continues to display the minimum value of the quantity of thereceived light that is renewed at each predetermined term. At the sametime, the first display portion 23 displays the current threshold value.

[0132] When the display select switch 32 is pushed in Step S13, it isdetermined whether the display select switch 32 was pushed in Step S14.If so, then the flow proceeds to Step S15. The display of the seconddisplay portion 22 is then changed from the minimum value of thequantity of the received light to the detection ratio of the currentquantity of the received light with respect to the threshold value. Atthis time, the first display portion 23 maintains its display of thecurrent threshold value. On the other hand, when the display selectswitch 32 is not pushed in Step S13, it is determined whether or not thedisplay select switch 32 was pushed in Step S14. If not, the flowreturns to Step S13 to keep the minimum value of the quantity of thereceived light as the display on the second display portion 22.

[0133] When the second display portion 22 displays the detection ratioand the display select switch 32 is determined to have been pushed inStep S16, the display of the second display portion 22 is changed fromthe detection ratio to the minimum value of the detection ratio at eachpredetermined term in Step S17. At this time, the first display portion23 maintains its display of the current threshold value. On the otherhand, when the display select switch 32 is determined not to have beenpushed in Step S16, the flow returns to Step S15 to keep the detectionratio as the display on the second display portion 22.

[0134] When the second display portion 22 displays the minimum value ofthe detection ratio and it is determined that the display select switch32 was pushed in Step S18, the display of the second display portion 22is changed from the minimum value of the detection ratio to the currentquantity of the received light in Step S19. At this time, the firstdisplay portion 23 maintains its display of the current threshold value.On the other hand, when it is determined that the display select switch32 was not pushed in Step S18, the flow returns to Step S17 to keep theminimum value of the detection ratio as the displayed numerals on thesecond display portion 22.

[0135] When the second display portion 22 displays the current quantityof the received light and the display select switch 32 is determined tohave been pushed in Step S20, the display of the second display portion22 is changed from the current quantity of the received light to theminimum value of the quantity of the received light at Step S13. At thistime, the first display portion 23 maintains its display of the currentthreshold value. On the other hand, when it is determined that thedisplay select switch 32 was not pushed in Step S20, the flow returns toStep S19 to keep the current quantity of the received light as thedisplay on the second display portion 22.

[0136] In other words, the display of the second display portion 22 iscyclically changed from “the minimum value of the quantity of thereceived light” to “the detection ration” to “the minimum value of thedetection ratio” to “the quantity of the received light” and then backto “the minimum value of the quantity of the received light” in turn bypushing the display select switch 32.

[0137]FIG. 7 is a flowchart showing a subroutine interrupting the mainroutine described in FIG. 6 in accordance with the first embodiment ofthe present invention. When the hold mode is carried out based on theflowchart shown in FIG. 6 and the display select switch 32 is pushed forthree seconds or more, the second display portion 22 displays “thecurrent quantity of the received light” and the first display portion 23displays “the current threshold value”.

[0138] In other words, when the display select switch 32 is pushed forthree seconds or more at any step of the hold mode, the hold mode isshifted to the first mode comprising the first display portion 23displaying the current threshold value and the second display portion 22displaying the current quantity of the received light.

[0139]FIG. 10 is a schematic representation of how the second displayportion can change in accordance with the first embodiment of thepresent invention.

[0140] For example, when the current numerals corresponding to thecurrent quantity of received light is “1234” and the display conditionof the second display portion is for the numerals corresponding to thequantity of received light, the second display portion displays “1234”as shown in the upper portion of FIG. 10.

[0141] Further, the second display portion has three indicator lightscomprising a first indicator light for the peak hold mode (PH), a secondindicator light for the bottom hold mode (BH) and a third indicatorlight for the detection ratio (%).

[0142] Therefore, when the second display portion displays “1234” as thecurrent numerals corresponding to the current quantity of receivedlight, all of the three indicator lights are off.

[0143] When the display select switch 32 is pushed by the operator, theabove mentioned first mode of the second display portion is changed andthe second display portion displays “123” as shown in lower portion ofFIG. 10.

[0144] In this situation, since the second display portion is showingthe detection ratio, the third indicator light (%) is turned on.

[0145] On the other hand, for the case of the second mode, when thesecond display portion displays “1234” as the current numeralscorresponding to the current quantity of received light as shown in theupper portion of FIG. 10 and the display select switch 32 is pushed, thesecond display portion displays the maximum or minimum value of thequantity of received light as shown in the right portion of FIG. 10.Also, the respective first or second indicator light corresponding tothe selected value is illuminated.

[0146] When the display select switch 32 is pushed again, the seconddisplay portion numerically displays the detection ratio and turns onthe third indicator light.

[0147] Additionally, when the display select switch 32 is pushed yetagain, the second display portion displays the maximum or minimum valueof the detection ratio as shown in the left portion of FIG. 10. Also,the respective first or second indicator light corresponding to theselected value is illuminated while continuing to illuminate the thirdindicator light.

[0148]FIG. 8 is a graph with an abscissa axis indicating time and anordinate axis indicating the quantity of received light to explain oneprinciple related to the hold mode. The graph shown in FIG. 8 is aschematic graph of the quantity of received light based on time.

[0149] As shown in FIG. 8, the quantity of received light from thepredetermined detectable area is not constant. This is because thequantity of received light changes based on whether the object 500 iswithin the detectable area or not.

[0150] For example, when the maximum quantity of the received light isdetected during one measurement period, a value indicating the maximumvalue (Maximum 1 in this figure) is stored in a memory installed in thephotoelectric sensor. Then the maximum value can be numericallydisplayed on the second display portion 22.

[0151] On the other hand, when the minimum quantity of the receivedlight is detected during one measurement period, a value indicating theminimum value (Minimum 1 in this figure) is stored in the memoryinstalled in the photoelectric sensor. Then the minimum value can benumerically displayed on the second display portion 22.

[0152] This process of determining the maximum value and the minimumvalue is repeated for each measurement period and the maximum andminimum values from the preceding measurement period are used to displayduring the subsequent measurement period.

[0153] In this embodiment, this hold mode function is carried out byusing the program installed into the CPU 201 of the main body unit 2.However, this hold mode function can also be carried out by the otherhold mode circuit and a hold mode time limit circuit instead of theprogram installed in the CPU 201.

[0154] Further, the predetermined term for holding the maximum value andthe minimum value includes a term predetermined by the sensormanufacture and memorized into the CPU 201. This term can be changedbased on the request of the operator.

[0155] In the first embodiment, the detection ratio is displayed on thedetection ratio display portion 12 of the head unit 1. Therefore, evenwhen the main body unit 2 is disposed at a location that is a longdistance from the head unit 1, the operator can adjust the position ofthe head unit 1 by checking the display of the detection ratio displayportion 12 of the head unit 1.

[0156] Accordingly, the operator can adjust the position of the headunit 1 easily and precisely so it can provide a detection ratio higherthan 1 (100%) when the object 500 is within the predetermined detectablearea and a detection ratio lower than 1 (100%) when the object is notwithin the predetermined detectable area.

[0157] Therefore, the operational efficiency of the adjustment of thehead unit 1 can be improved.

[0158] Furthermore, since the detection ratio display portion 12 of thehead unit 1 displays the detection ratio, it is easy to confirm whetheror not the photoelectric sensor stably detects the object 500 withoutchecking the display portion of the main body unit 2.

[0159] Since the detection ratio calculated by the CPU 201 of the mainbody unit 2 is transferred to the head unit 1 as the variable voltage VAusing the power supply voltage of the head unit 1, it is not necessaryto add an additional signal line for sending the detection ratio.

[0160] In the first embodiment, the detection ratio is expressed by theratio of the level LV corresponding to the quantity of received lightwith respect to the threshold value TH. However, the detection ratio canalso be expressed as the difference between the level LV correspondingto the quantity of received light and the threshold value TH.

[0161] Further, in the first embodiment, the sensor has the laser diode102 as the emitting element of the light emitting portion. However, thesensor can use an LED as the emitting element. Furthermore, in the firstembodiment, the detection ratio display portion 12 of the head unit 1uses a bar type of display comprised of a plurality of LEDs 12 a, 12 band 12 c. However, the detection ratio display portion 12 of the headunit 1 can also use other types of displays that can indicate anumerical value corresponding to the value of the detection ratio.

[0162] According to the above-mentioned first embodiment, thephotoelectric sensor of the present invention is a reflective typesensor. However, the sensor of the present invention can also be adaptedto a thru-beam type sensor. In this case, the head unit comprises aseparate light emitting head unit and a separate light receiving headunit.

[0163] The light emitting head unit has the laser driving circuit 101and the laser diode 102. The light receiving head unit has thephoto-diode 104, the light receiving circuit 105, the fixed power supplycircuit 106, the LED lighting circuit 107 and the detection ratiodisplay portion 12. Further, it is also preferred that the lightemitting head unit can have the detection ratio display portion 12.

[0164] The sensor of the present invention can also adapt to aphotoelectric sensor using the triangulation principle.

[0165]FIG. 11 is a schematic diagram showing the head unit of thephotoelectric sensor using the triangulation principle as a secondembodiment of the present invention.

[0166] In FIG. 11, a head unit 800 has a LED 801, a light emitting lens802, a light receiving lens 803 and a Position Sensing Device (PSD) 804.

[0167] The reflected light from the object 900 is received on areceiving light surface of the PSD 804 as a light spot after passingthrough the light receiving lens 803.

[0168] The position of the light spot on the receiving light surface ofthe PSD 804 is changed based on the distance between the photoelectricsensor 800 and the object 900.

[0169] When the object 900 is close to the sensor 800, the light spot isformed on a side e1 of the light receiving surface of the PSD 804. Onthe other hand, when the object 900 is away from the sensor 800, thelight spot is formed at the other side e2 of the light receiving surfaceof the PSD 804.

[0170] The PSD 804 outputs two light receiving signals N and Fcorresponding to the position of the light spot on the surface of thePSD 804.

[0171] The signal N has a level (current value) which is proportional toa distance between the edge portion e1 of the surface of the PSD 804 andthe light spot and the other signal F has a level (current value) whichis proportional to a distance between the edge portion e2 of the surfaceof the PSD 804 and the light spot.

[0172] Accordingly, the distance between the sensor 800 and the object900 can be detected by the two signals N and F.

[0173] An angle of incidence of the reflected light from the object 900which can be incident on the light receiving surface of the PSD 804becomes the detectable area on an optical axis of the emitting lightfrom the LED 801.

[0174] A predetermined setting position ST is set within the detectingrange and the side closer to the sensor 800 corresponding to the settingposition ST becomes the detectable region or area and the side fartherfrom the sensor 800 located past the position ST becomes theundetectable region or area. When the PSD 804 receives the reflectedlight from the detectable area, the sensor 800 detects the existence ofthe object 900.

[0175]FIGS. 12A and 12B are graphs explaining the process of determiningthe existence of the object using the signals N and F output from thePSD 804.

[0176] The difference between N and F corresponds to the position of thedetectable object 900 disposed within the detectable area.

[0177] In actual processing, the differences between the positionsignals (N−F) divided by the sum of the position signal (N+F)corresponds to all of the quantity of received light and gives theposition signal {(N−F)/(N+F)}.

[0178] This positioning signal becomes the positioning informationindicating the position of the object 900 within the detectable area.

[0179] As shown in FIG. 12A, when the level LV of the positioning signalis equal to or higher than the predetermined threshold value TH, it isdetermined that the object 900 is disposed within the detectable area.On the other hand, as shown in FIG. 12B, when the level LV of thepositioning signal is lower than the value TH, it is determined that theobject 900 is not disposed within the detectable area.

[0180] An adjustment of the threshold value TH can move the settingposition ST disposed within the detecting range.

[0181] In the case of the photoelectric sensor shown in FIG. 11, a ratioof the level LV of the positioning signal with respect to the thresholdvalue TH becomes the detection ratio.

[0182] In the case shown in FIG. 12A, the detection ratio indicates avalue larger than “1”. On the other hand, in the case shown in FIG. 12B,the detection ratio indicates a value smaller than “1”.

[0183] When the object 900 is disposed far from the setting position STand is disposed within the detectable region, the detection ratiobecomes a value larger than “1”.

[0184] Further, as stated above, the main body unit of the photoelectricsensor of the present embodiment has the first display portion 23 andthe second display portion 22. The second display portion can displaythe positioning information, the detection ratio, the maximum or minimumvalues, the threshold value and the maximum or minimum value of thedetection ratio selectively.

[0185] The first display portion 23 displays the threshold value.

[0186] The remaining structures of the sensor of the second embodimentof the present invention are substantially the same as the structures ofthe sensor described in the first embodiment of the present inventionand shown in FIGS. 1 though 4.

[0187] The detection ratio display portion of the head unit 800 of thesecond embodiment displays the detection ratio. Therefore, even when themain body unit is disposed at a long distance from the head unit 800,the operator can adjust the position of the head unit 800 by checkingthe display of the detection ratio display portion in the head unit 800.

[0188] Accordingly, when the object 900 is disposed within thedetectable region of the detecting range, the detection ratio becomeslarger than “1” and when the object 900 is not disposed within thedetectable region, the detection ratio becomes smaller than “1”.Therefore, it is easy to precisely adjust the position of the headportion 800. Further, this provides operational efficiency for adjustingthe position of the head portion 800.

[0189] In these embodiments, the detection ratio can be also expressedby a difference between the level LV of the position signal and thethreshold value TH.

[0190] In such a case, the detection ratio expresses a displacement ofthe object 900 relative to the setting position ST.

[0191]FIG. 13 is a perspective view of a sensor head unit 1A of aphotoelectric sensor of a separate type in accordance with a thirdembodiment of the present invention.

[0192] The main body unit (not shown) connected to the sensor head unit1A shown in FIG. 13 is substantially the same as the main body unit ofthe sensor shown in FIG. 1.

[0193] As shown in FIG. 13, an upper surface of the casing 11 of thehead unit 1A has a first additional display portion 12B similarlycorresponding to the first display portion 23 of the main body unit 2and a second additional display portion 12A similarly corresponding tothe second display portion 22 of the main body unit 2.

[0194] The first additional display portion 12B comprises four digitnumber display portions each of which comprises seven segments tonumerically display the quantity of received light or the detectionratio.

[0195]FIG. 14 is a block diagram showing a structure of the separatetype photoelectric sensor shown in FIG. 13.

[0196] The differences between the sensor shown in FIG. 14 and thesensor shown in FIG. 2 are that the sensor head unit 1A shown in FIG. 14has an A/D converter 121 and a seven segment display circuit 122 insteadof the LED lighting circuit 107 of the sensor shown in FIG. 2.

[0197] A variable voltage VA is provided to an A/D converter 121 from avariable power source circuit 204 of the main body unit 2 to the headunit la though the cable 31 a.

[0198] Further, a standard voltage Vref is provided from the fixed powercircuit 106 to the A/D converter 121 and the seven segment displaycircuit 122.

[0199] The A/D converter 121 converts the variable voltage VA to adigital signal indicating the detection ratio and the digital signal isprovided to the display circuit 122.

[0200] The seven segment display circuit 122 displays numeralscorresponding to the digital signal on the first additional displayportion 12B which comprises four digit number display portions each ofwhich comprises seven segments to display the detection ratio.

[0201] In the case of the photoelectric sensor of this embodiment, sincethe detection ratio calculated by the CPU 201 of the main body unit 2 istransferred to the head unit 1A as the variable voltage VA using thepower supply voltage of the head unit 1A, it is not necessary to use anadditional signal line for sending the signal indicative of thedetection ratio.

[0202] In this embodiment, the first additional display portion 12B canselectively display the detection ratio and the quantity of thereceiving light.

[0203] In this case, it is preferred that the head unit 1A have a selectswitch to select the display of the first additional display. Further,the second additional display portion 12A can numerically display thethreshold value.

[0204]FIG. 15 discloses an integrated photoelectric sensor 520 accordingto a further embodiment of the present invention. The sensor 520includes an upper surface of a casing 521 that has a first displayportion 523, a second display portion 522, a bar LED monitor 524, alaser emission indicator 525, hold mode indicators 527A and 527B, anadjustment switch 528, a setting switch 529 and a display select or modeswitch 532. The other elements of the sensor head unit 1 discussed inconnection with FIG. 1 are also incorporated into the integrated sensor520. The main difference is that the emitting portion and the receivingportion are incorporated into the sensor 520. The sensor 520 operates ina very similar fashion as that shown in FIG. 1.

[0205] As shown in FIG. 16, the main body unit 2 of the photoelectricsensor can also display several different types of modes other thanthose discussed above. These different types of modes include a “PowerSetting Mode” for setting the kind of light emitting amount; a“Detection Method Setting Mode” for setting the detection pointcorresponding to normal detection work, including up edge detection anddown edge detection; a “Hold Setting Mode” for setting the maximum valueor the minimum value corresponding to the received light amount withinevery predetermined detection cycle and the detection ratio within everypredetermined detection cycle as described above in connection withFIGS. 9A through 9C; and a “Timer Setting Mode” for setting severaltypes of timers.

[0206] These modes are cyclically displayed by pushing the displayselection switch (also labeled “MODE”) as shown in FIG. 16. In detail,when the display selection switch is pushed for three seconds or more,the numeric display shown on the second display portion is changed from“the value indicative of the received light amount” or “the valueindicative of the detection ratio” as shown at STEP (A) to “turb”indicating the current mode which is a “Power Setting Mode” as shown atSTEP (B). Then, at the same time, the display of the first displayportion can also be changed from “the value indicative of the threshold”to “different types of marks indicative of the kind of power mode”.

[0207] In detail, as shown in FIG. 17, the power setting mode has threedifferent kinds of power modes, called “FINE”, “TURBO” and “SUPER”.According to the present embodiment, the “FINE” condition is adapted todetect a target (object) having a high speed of movement in thedetectable area and the condition is indicated in the display as “-F” onthe first display portion. The “TURBO” condition is used during regulardetection work. This “TURBO” condition is indicated by “--t” on thefirst display portion. Further, the “SUPER” condition is used to detectthe target (object) when there is an insufficient light amount. This“SUPER” condition is indicated by “---S” on the first display portion.

[0208] When the display enters STEP (B), the first display portiondisplays “-F” because the sensor is predetermined to display this as aninitial display or if other condition like “TURBO” or “SUPER” conditionis set previously at this mode, the previous set condition is displayedas the initial display. The operator can then select one desirablecondition by using the adjustment switch (UP and DOWN Switch), sincepushing the adjustment switch can cyclically change the display of theseconditions on the first display portion. Further, since the adjustmentswitch comprises up and down buttons, the display shown on the firstdisplay portion can switch back and forth between “-F” and “--t”, “--t”and “---S”, and “---S” and “-F”.

[0209] Then, when the operator selects one of these conditions, pushingthe display select switch for less than three seconds completes thesetting of the power setting mode. By this action, the power settingmode is shifted to the detection method setting mode as shown in STEP(C) of FIG. 16.

[0210] At that time, as shown in FIG. 18, the display of the seconddisplay portion is changed from “turb” to “dEtc” which means“detection”. Further, the first display portion displays “std” as aninitial setting condition or a previous selected condition similar tothat system described above in connection with the power setting mode.The “std” displayed condition is adapted for regular detection work. The“┘⁻d” displayed condition is adapted for detecting the edge of upwardmovement of the received light amount and the “┐_d” condition is adaptedfor detecting the edge of downward movement of the received lightamount. The operator then selects one of these desired conditions byusing the adjustment switch. Further, since the adjustment switchcomprises up and down buttons, the display of the first display portion23 can move back and forth between the “std” and “┘⁻d”, “┘⁻d” and “┐_d”and “┐_d” and “std” conditions. Then, when the operator selects onecondition, the detection method setting mode is completed by pushing thedisplay select switch for less than three seconds while the desiredcondition is displayed. Then, by this action the detection methodsetting mode is shifted to the hold setting mode as shown at STEP (D).

[0211] At that time, as shown in FIGS. 9A through 9C, the display of thesecond display portion is changed from “dEtc” to “dsp”. The term “dsp”means “display” and the first display portion displays “std” as aninitial setting condition or a previously selected condition similar tothat system described above in connection with the power setting mode.The “std” condition is indicated as the “No hold condition”. The “PH”condition is adapted to hold a peak value (maximum value) correspondingto at least the received light amount or the detection ratio at everypredetermined detection cycle. Further, the “bH” condition is adapted tohold a bottom value (minimum value) corresponding to at least thereceived light amount or the detection ratio at every predetermineddetection cycle. The operator then selects one of the desired conditionsby using the adjustment switch 28. Further, since the switch 28comprises up and down buttons, the display of the first display portion23 can move back and forth between each of the above-mentionedconditions. *

[0212] Then, when the operator selects one of these conditions, pushingthe display select switch less than three seconds while the desiredcondition is displayed completes the hold setting mode. Then, the holdsetting mode is shifted to the timer setting mode as shown at STEP (E)of FIG. 16.

[0213] At that time, as shown in FIG. 19, the display of the seconddisplay portion is changed from “dsp” to “dly”. The “dly” display means“delay” and the first display portion displays “off” as an initialsetting condition or a previous selected condition. The “oFF” conditionindicates that the timer function is turned off. In other words, thesensor operates regularly.

[0214] The “oF-d” condition means an “off delay timer condition” whichis a first timer function. When the sensor detects the received lightsignal, an “OFF” output signal corresponding to the light detection isoutput with a delay to an outside machine. The delay is caused by apreset timer for a length that is determined by the operator. How thelength of the timer is set will be described below.

[0215] Further, the “on-d” condition indicates an “on delay timercondition” and is a second timer function. When the sensor detects thereceived light signal, an “ON” signal is sent to an outside machine asthe output signal corresponding to the detection with a delay that iscaused by the preset timer set by the operator.

[0216] Furthermore, the “on-S” condition indicates a “one shot timercondition” and is a third timer function. After the sensor detects thereceived light signal, an “ON” signal is sent to an outside machine.Then an “OFF” signal is subsequently sent to the outside machine with adelay that is caused by the preset timer set by the operator.

[0217] The operator then selects one desired condition by using theadjustment switch. Further, since the switch comprises up and downbuttons, the display of the first display portion can move back andforth between each of the above-mentioned conditions.

[0218] Then, when the operator selects one condition, pushing thedisplay select switch less than three seconds while the desiredcondition is displayed completes the timer setting mode. If the operatorselects the “oFF” condition, meaning of no timer is used, the flowreturns to STEP (A) automatically. All of the mode setting functionshave then been carried out so all of the set modes are then used and thedisplays of the first and second display portions return back to theirprevious conditions.

[0219] On the other hand, when the operator selects another timercondition from the “OFF Delay”, “ON Delay” and “ONE Shot” conditions,the timer setting mode is shifted to a time setting mode as shown atSTEP (F) of FIG. 16.

[0220] As shown in FIG. 20, when the timer setting mode is displayed,the second display portion displays “t” indicating “time” and the firstdisplay portion displays “1” as an initial setting condition or displaysa previously selected number.

[0221] According to the present embodiment, since the device can set thetimer length between 1 microsecond and 9999 microseconds, the operatordisplays and sets the desired value by using the adjustment switch. Whenthe delay time setting is completed and the display select switch 32 ispushed for less than three seconds, the flow returns to STEP (A) of FIG.16 automatically. Then all of the mode setting functions have beencarried out so all of the set modes are then used and the displays ofthe first and second display portions return back to their previousconditions.

[0222] According to the above described function modes shown in FIG. 16through FIG. 20, since each of the first and second display portions 23and 22 do not have a large number of display segments, the displayportions 23 and 22 can display marks, alphabet letters or somecombination of several alphabet letters which can be associated with theregular name of the mode that should be set and the regular name of thecondition, respectively.

[0223] It is to be understood that although the present invention hasbeen described with regard to preferred embodiments thereof, variousother embodiments and variants may occur to those skilled in the art,which are within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

What is claimed is:
 1. A photoelectric sensor comprising: a sensor unithaving a casing, said casing including one surface having a firstdisplay and a second display, said first display being structured andarranged to display a threshold value that may be set by an operator ofsaid photoelectric sensor, said second display being structured andarranged to display actual conditions sensed by said photoelectricsensor; and a selection device for selecting different operationalvalues to display on said second display, wherein said selection deviceincludes a mechanism disposed on said casing for changing the differentoperational values on said second display.
 2. A photoelectric sensor asdefined in claim 1, further comprising an adjustment switch foradjusting the threshold value displayed on said first display whiledisplaying at least one actual condition on said second display.
 3. Aphotoelectric sensor as defined in claim 1, wherein said sensor unit isa main body unit and said photoelectric sensor further comprises asensor head unit disposed apart from and operatively connected to saidmain body unit.
 4. A photoelectric sensor as defined in claim 3, whereinsaid sensor head unit includes an outer casing, said outer casingincluding one surface having a first head unit display and a second headunit display, said first head unit display being structured and arrangedto display a property set by an operator of said photoelectric sensorand said second head unit display being structured and arranged todisplay actual conditions sensed by said photoelectric sensor.
 5. Aphotoelectric sensor as defined in claim 1, wherein said mechanismincludes a mode selection switch for changing the different operationalvalues on said second display.
 6. A photoelectric sensor as defined inclaim 5, wherein said mode selection switch has a first operational modethat switches the display based on a first switch depression length anda second operational mode that switches to a different type of displaybased on a second switch depression length that is longer than the firstswitch depression length.
 7. A photoelectric sensor as defined in claim1, wherein said sensor unit includes an emitting portion and a receivingportion disposed in said casing.
 8. A photoelectric sensor as defined inclaim 7, wherein said emitting portion is separate from said receivingportion.
 9. A photoelectric sensor as defined in claim 1, furthercomprising a CPU for processing information and determining the actualconditions sensed by said photoelectric sensor, said CPU being capableof determining a value indicative of an actual amount of light receivedby said photoelectric sensor and a detection ratio, the detection ratiobeing a ratio of the threshold value and the actual amount of lightreceived by said photoelectric sensor, said CPU being operativelyconnected to said second display to cyclically display the valueindicative of the actual amount of light received by said photoelectricsensor and the detection ratio on said second display.
 10. Aphotoelectric sensor as defined in claim 1, further comprising a CPU forprocessing information and determining the actual conditions sensed bysaid photoelectric sensor; said CPU being capable of determining a valueindicative of a maximum amount of light received by said photoelectricsensor in a predetermined preceding measurement period, a detectionratio, a maximum value of the detection ratio in the predeterminedpreceding measurement period and a value indicative of an amount oflight received by said photoelectric sensor, the detection ratio being aratio of the threshold value and the actual amount of light received bysaid photoelectric sensor; said CPU being operatively connected to saidsecond display to cyclically display the value indicative of the maximumamount of light received by said photoelectric sensor in thepredetermined preceding measurement period, the detection ratio, themaximum value of the detection ratio in the predetermined precedingmeasurement period and the value indicative of an amount of lightreceived by said photoelectric sensor, on said second display.
 11. Aphotoelectric sensor as defined in claim 1, further comprising a CPU forprocessing information and determining the actual conditions sensed bysaid photoelectric sensor, said CPU being capable of determining a valueindicative of a maximum amount of light received by said photoelectricsensor in a predetermined preceding measurement period, a valueindicative of a minimum amount of light received by said photoelectricsensor in the predetermined preceding measurement period, a detectionratio, a maximum value of the detection ratio in the predeterminedpreceding measurement period, a minimum value of the detection ratio inthe predetermined preceding measurement period and a value indicative ofan amount of light received by said photoelectric sensor, the detectionratio being a ratio of the threshold value and the actual amount oflight received by said photoelectric sensor; said CPU being operativelyconnected to said second display to selectively display at least one ofthe value indicative of the maximum amount of light received by saidphotoelectric sensor in the predetermined preceding measurement period,the value indicative of the minimum amount of light received by saidphotoelectric sensor in the predetermined preceding measurement period,the detection ratio, the maximum value of the detection ratio in thepredetermined preceding measurement period, the minimum value of thedetection ratio in the predetermined preceding measurement period andthe value indicative of an amount of light received by saidphotoelectric sensor, on said second display.
 12. A photoelectric sensoras defined in claim 1, further comprising a CPU for processinginformation, said CPU including: a first display mode for displaying avalue indicative of an amount of light received by said photoelectricsensor and a value indicative of a detection ratio, the detection ratiobeing a ratio of the threshold value and the amount of light received bysaid photoelectric sensor, and a second display mode for displaying avalue indicative of the amount of light received by said photoelectricsensor and a value indicative of at least one of a maximum and minimumamount of received light within a predetermined preceding measurementperiod; and wherein operation of said selection device changes thedisplay of said second display between the first and second displaymodes.
 13. A photoelectric sensor as defined in claim 1, furthercomprising a CPU for processing information, said CPU including: a firstdisplay mode for displaying a value indicative of an amount of lightreceived by said photoelectric sensor and a value indicative of adetection ratio, the detection ratio being a ratio of the thresholdvalue and the amount of light received by said photoelectric sensor, anda second display mode for displaying a value indicative of the amount oflight received by said photoelectric sensor and a value indicative of atleast one of a maximum and minimum amount of the detection ratio withina predetermined preceding measurement period; and wherein operation ofsaid selection device changes the display of said second display betweenthe first and second display modes.
 14. A photoelectric sensorcomprising: a sensor unit having a casing, said casing including onesurface having a first display and a second display, said first displaybeing structured and arranged to display a threshold value that may beset by an operator of said photoelectric sensor, said second displaybeing structured and arranged to display actual conditions sensed bysaid photoelectric sensor; and an adjustment switch disposed on saidcasing, said adjustment switch allowing adjustment of the thresholdvalue shown on said first display while said second display shows atleast one of the actual conditions sensed by said photoelectric sensor.15. A photoelectric sensor as defined in claim 14, further comprising aselection device for selecting different operational values to displayon said second display, wherein said selection device includes amechanism disposed on said casing for changing the different operationalvalues on said second display.
 16. A photoelectric sensor as defined inclaim 14, wherein said sensor unit is a main body unit and saidphotoelectric sensor further comprises a sensor head unit disposed apartfrom and operatively connected to said main body unit.
 17. Aphotoelectric sensor as defined in claim 16, wherein said sensor headunit includes an outer casing, said outer casing including one surfacehaving a first display and a second display, said first display beingstructured and arranged to display a property set by an operator of saidphotoelectric sensor and said second display being structured andarranged to display actual conditions sensed by said photoelectricsensor.
 18. A photoelectric sensor comprising: a main body unit and asensor head unit connected by at least one cable, at least one of saidmain body unit and said sensor head unit including a casing, said casingincluding one surface having a first display and a second display, saidfirst display being structured and arranged to display a property set byan operator of said photoelectric sensor, said second display beingstructured and arranged to display actual conditions sensed by saidphotoelectric sensor; and a selection device for selecting differentoperational values to display on said second display, wherein saidselection device includes a mechanism disposed on said casing forchanging the different operational values on said second display.
 19. Aphotoelectric sensor as claimed in claim 18, wherein said mechanismincludes a mode selection switch for changing the different operationalvalues on said second display.
 20. A photoelectric sensor as claimed inclaim 18, wherein both said main body unit and said sensor head unitrespectively include a casing, both of said casings including onesurface having a first display and a second display, said first displaybeing structured and arranged to display a property set by an operatorof said photoelectric sensor, said second display being structured andarranged to display actual conditions sensed by said photoelectricsensor.
 21. A photoelectric sensor comprising: a main body unit and asensor head unit connected by at least one cable, at least one of saidmain body unit and said sensor head unit including a casing, said casingincluding one surface having a first display and a second display, saidfirst display being structured and arranged to display a property set byan operator of said photoelectric sensor, said second display beingstructured and arranged to display actual conditions sensed by saidphotoelectric sensor; and an adjustment switch disposed on said casing,said adjustment switch allowing adjustment of the threshold value shownon said first display while said second display shows at least one ofthe actual conditions sensed by said photoelectric sensor.
 22. Aphotoelectric sensor as defined in claim 21, further comprising aselection device for selecting different operational values to displayon said second display, wherein said selection device includes amechanism disposed on said casing for changing the different operationalvalues on said second display.
 23. A photoelectric sensor comprising: asensor unit having a casing, said casing including one surface having afirst display and a second display, said sensor having a plurality ofdifferent function setting modes having several conditions, said firstdisplay displaying the function setting modes and when the first displaydisplays one of the different function setting modes, the second displaydisplays one of the several conditions corresponding to the displayedfunction setting mode on the first display; and a selection device forselecting the different function setting modes including a power settingmode and a timer setting mode, each of the power setting mode and thetimer setting mode having a plurality of displayable conditions.
 24. Aphotoelectric sensor as defined in claim 23, wherein the sensor furtherhaving a normal mode for displaying a threshold value, the thresholdvalue being a value indicative of the actual amount of light received,and means for allowing an operator to select which of the first andsecond displays will display the threshold value and which of the firstand second displays will display at least one of an actual amount oflight received by the sensor and a detection ratio, the detection ratiobeing a value determined based on the actual amount of light received bythe sensor and the threshold value, wherein the means for allowing anoperator to select which of the first and second displays will displaythe at least one of the actual amount of light received by the sensorand the detection ratio includes cyclically selecting to display theactual amount of light received by the sensor and the detection ratio.25. A photoelectric sensor as defined in claim 23, wherein the differentdisplay setting modes further includes a hold setting mode having aplurality of displayable conditions.
 26. A photoelectric sensor asdefined in claim 23, further comprising a means for automaticallyreturning said first and second displays to a previous display that wasshown prior to entering the different display setting modes.
 27. Aphotoelectric sensor as defined in claim 23, further comprising a meansfor automatically returning said first and second displays to a previousdisplay that was shown prior to entering the different display settingmodes when the timer setting mode is not selected.
 28. A photoelectricsensor as defined in claim 27, further comprising a means for selectinga timer delay when the timer setting mode is selected.